It has been found that relief from localized pain can be achieved in many patients through the delivery of electrical stimulation or high-frequency signals to a target region. To accomplish this, stimulation or radio-frequency electrodes are placed within a patient's body. Those electrodes are connected to a generator of stimulation electrical signals or high-frequency electrical signals to deliver energy to tissue and neural structures. This can result in anesthesia, temporary relief, or long-term relief from pain. Examples of electrodes, signal generators, and methods usable for this purpose can be found in the product line of Radionics, Inc., of Burlington, Massachusetts.
A wide variety of electrode geometries can be used in such applications. For example, an electrode unit having an insulated shaft and an exposed electrical tip, which can be pointed, blunt and rounded, or open, are suitable for various procedures. Pointed tips are self-penetrating, while rounded tips can be used in soft tissue such as the brain. Open tips can be used to deliver a liquid or other diagnostic or therapeutic agent, or a stylet or an endoscopic tool, to the target while simultaneously performing electrical treatment. Radio-frequency electrodes are commonly used; these typically have an insulated straight tubular metal shaft with an electrically exposed tip. Connection at the hub or proximal end of the electrode is made to an external signal generator capable of generating stimulation or high-frequency energy. In the course of treatment, the electrode is inserted into the patient's tissue, and signals from the signal generator are thereby delivered into the region of the patient's tissue surrounding the tip of the electrode.
The SMK Needle electrodes from Radionics are in some ways representative of electrodes typically used in pain relief procedures. The SMK Needles have plastic hubs and metal shafts that are insulated over most of their length. An exposed tip is a straight extension of the metal tubing shaft of the needle. An obdurating stylet is inserted into the needle during insertion into the patient's tissue. Once it has been inserted, the stylet is withdrawn and the radio-frequency or stimulation probe is inserted. The probe is connected to an external signal generator. Contrast agents or anesthetic fluids can be injected into the tissue near the tip through the hollow needle.
A common use for the Radionics SMK Needle is in the stimulation and denervation of a patient's spine. In this procedure, the SMK Needle electrodes are inserted, while viewed via X-ray or fluoroscope, near the facet joints or other neural structures of the spine. Anesthetic or diagnostic localization agents can be injected through the needles, and stimulation testing can then be performed. Radio-frequency heat ablation of a portion of the patient's tissue near the tip of a needle is routinely performed. Hence, proper placement of the needle tip in the complicated structure of a patient's spine requires great skill by the treating clinician. One limitation of the straight electrodes typically used in such procedures is that the needles may need to be withdrawn and re-inserted multiple times to achieve the proper target region for the needle tip.
The need to access other complex structures, such as lumbar-sacral discs, particularly where there is a high pelvic brim in males and in those individuals having extreme degenerative narrowing, makes needle placement even more difficult. The nerve root in the lower spine may be accidentally impaled; this presents a serious medical risk to the patient. Again, the use of straight, self-penetrating needles is limited somewhat in that the tip is collinear with the needle shaft, so navigating the tip to avoid critical structures requires redirection of the shaft and repeated manipulation. It would be desirable to facilitate such redirection in ways unachievable by a straight needle, reducing the need to withdraw and reinsert the needles.
Moreover, the straight, exposed tip of a straight needle cannot hug the contour of a curved bony structure such as the superior articular facet, which proximates target nerves. This can present a restriction to target location in some situations.
It is desirable to be able to redirect or steer the tip of the electrode, which for straight needles can be tedious and difficult. It is further desirable to be able to control the tip of a needle by mere shaft rotation or other means of manipulation.
Stimulation and high frequency electrodes having expandable and flexible curved tips are known. Examples of such electrodes are the TEW Electrode Kit and the ZHK Electrode Kit, both manufactured by Radionics. Those electrodes both have flexible, curved tips, which extend from the straight shaft of an enclosing cannula to extend off-axis in an arc. This is useful in certain neural regions such as the trigeminal ganglion or the pituitary gland, or any area where the target region is very soft or fluid filled. Such flexible off-axis electrodes have a limitation that there tips cannot penetrate tough tissue or encounter hard bone without being damaged or diverted.
It is observed that neither straight needles nor flexible electrodes have the desired characteristics for use in difficult-to-reach target regions. Accordingly, it would be desirable to have an electrode cannula for stimulation or ablation that avoids the limitations of the art.